The arithmetic sequence $(a_i)$ is defined by the formula: $a_i = 3 + 2(i - 1)$ What is $a_{10}$, the tenth term in the sequence?
Explanation: From the given formula, we can see that the first term of the sequence is $3$ and the common difference is $2$ To find $a_{10}$ , we can simply substitute $i = 10$ into the given formula. Therefore, the tenth term is equal to $a_{10} = 3 + 2 (10 - 1) = 21$.